This invention relates to a semiconductor device and a method for manufacturing same in which the performance of the semiconductor device is improved. More particularly, this invention relates to measures for eliminating disadvantages caused by the effect of electrical shorts and shunts due to pinholes or other gaps created during the fabrication process of the device.
Recently, considerable efforts have been made to develop systems for depositing amorphous semiconductor alloys, each of which can encompass relatively large areas, and which can be doped to form p-type and n-type materials for the production of p-i-n and other type devices which are, in photovoltaic and other applications, substantially equivalent to their crystalline counterparts. As such devices, the applicant disclosed improved photoelectric cells in Japanese Patent Published Applications Nos. sho 55-4994, 55-124274, 56-13777, 56-13778 and 56-13779.
One example of a prior art photovoltaic device is shown in FIG. 1. In the figure, a transparent conductive film 2 is formed on a glass substrate 1 with a mask aligned above the substrate 1. Semiconductor layers 3 are deposited on the substrate 1 with the conductive film 2 therebetween with a mask aligned above the substrate 1. Further, on the substrate 1 with the conductive film 2 and the semiconductor layers 3, aluminum layers 4 are formed as second electrodes with the aid of a mask. Reference numerals 31 and 11 designate respective photoelectric cells in the figure.
The two cells 31 and 11 are connected in series by means of a connection 12. In the connection 12 the second electrode 38 is made in contact with the first electrode 37. Upper electrode 39 is connected to external connection 5. Although the figure appears only with two connections, a number of the cells are connected with each other in series. The integrated photovoltaic device tends to be degraded after thermal treatment at 150.degree. C. for tens of hours. Such device is not suitable for outdoor use where the device is likely subjected to high temperature ambience. Furthermore, it is impossible to perform the patterning of the aluminum layers 14 with laser processing instead of that with masks, since the laser beam is likely to injure the thin semiconductor film during processing. High efficiency of the patterning with masks cannot be expected due to low accuracy in aligning the masks with the pattern, there being enjoyed no self alignment.
Further, the voltage and current output of the thin film solar cells may be greatly reduced or completely eliminated by electrical shorts or shunts formed during the fabrication of the solar cell. Electrical shorts occur when there is a pinhole in the semiconductor layer and the front and back electrodes are in touching contact. A shunt is the loss of charge in the semiconductor body due to imperfect barrier formation or the formation of an ohmic contact by a high work function metal rather than a Schottky barrier formation. The problem of solar cell defects which cause shorts or shunts increase greatly with increasing solar cell size. If large area solar cells are to be economically feasible, methods of eliminating these shorts and shunts during fabrication or removing the defects after processing must be developed.